In the manufacture of semiconductor device, processing with lithography utilizing resists has been conventionally performed. This processing includes: forming a resist film on a semiconductor substrate such as a silicon wafer; irradiating the substrate with active light such as ultraviolet through a mask pattern having a pattern of the semiconductor device; and developing the substrate to obtain a resist pattern. The substrate is treated by etching with the obtained resist pattern as a protection film, so that concavities and convexities corresponding to the pattern are formed on the surface of the substrate.
In recent years, semiconductor devices become finer, and thus a wavelength of active light to be used becomes shorter from KrF excimer lasers (248 nm) to ArF excimer lasers (193 nm) and EUV light (13.5 nm). Accordingly, various effects such as the reflection of active light from a semiconductor substrate impede proper formations of resist patterns, disadvantageously.
To overcome such a disadvantage, a method is mainly used in which an underlayer film including an organic material, such as an anti-reflective coating and a flattening film, that is, an organic underlayer film, is formed between a semiconductor substrate and a resist. In this case, a portion of the organic underlayer film which is not protected with a resist is removed by etching with a resist pattern as a protection film, and then the semiconductor substrate is processed. Etching for processing organic underlayer films and semiconductor substrates is usually dry etching.
As an underlayer film between a semiconductor substrate and a photoresist, a hardmask that is known as a film including an inorganic material has been used. In this case, a photo resist (organic material) and a hardmask (underlayer film: inorganic material) are significantly different for their components, and thus, the rate of removal by dry etching largely depends on gas species used for dry etching. Therefore, a semiconductor substrate can be processed by utilizing the different etching rates. Generally, the processing of a semiconductor substrate is conducted by dry etching.
A multilayer resist process has also been developed, in which an organic underlayer film is formed as the underlayer of a hardmask by an application method, a CVD method, or the like, and dependency of the dry etching rates of a hardmask and an organic underlayer film on gas species is utilized.
The ArF liquid immersion lithography method has been also developed to lower the cost in the manufacture of semiconductors. In this method, a liquid medium such as water or a dedicated high refractive index liquid with specific thickness is placed between exposure light and a resist, so that the difference between refractive indices allows the ArF light to be further finer to form a pattern, and thus the processing method by using an ArF excimer laser is long-lasting. An inert gas such as air and nitrogen has been conventionally used as an exposure light passing space. In the liquid immersion lithography method, however, the exposure light passing space is substituted with a liquid medium having a refractive index (n) that is larger than the refractive index of such a space (gas), but smaller than the refractive index of a resist film. This method is advantageous because similarly to when exposure light having a shorter wavelength or a high NA lens is used, high resolution is achieved and a focal depth range is not decreased even when a light source having the same exposure wavelength is used. If the liquid immersion lithography is used, a resist pattern having high resolution and an excellent focal depth can be formed at lower cost by using a lens installed on a current exposure device.
ArF liquid immersion lithography is conducted such that a liquid such as water is directly brought into contact with a resist when the resist is exposed. Accordingly, a resist top protection film (top coating) for a liquid immersion process may be used on the resist, in order to prevent defects caused by elution of a foreign substance from the resist.
In a fine lithography process used for manufacturing semiconductor device in large scale, in particular, in a liquid immersion lithography by using an ArF excimer laser, a finer resist pattern is produced, and a specific step in which a liquid medium is directly brought into contact with the resist during exposure is employed. Thus, micro defects that have not conventionally been detected, and defects (watermark) caused by bubble contained in the chemical solution for lithography (A) (a resist, an organic resist underlayer film, a hardmask, a top coating, a developing solution, and the like) have been observed.
Semiconductor manufacturing apparatus used in a lithography process for manufacturing semiconductors include a coater (coating device) for coating a semiconductor substrate with the chemical solution for lithography (A), a developer (development device), and the like. When the chemical solution for lithography (A) is supplied to such devices, it is supplied via a supply system for the chemical solution for lithography (A), which is sealed from an external environment (clean room atmosphere). Usually, the chemical solution for lithography (A) is delivered as sealed. After the sealed chemical solution for lithography (A) is opened in a clean room, it is placed in a supply line for supplying the chemical solution for lithography (A) to a device, so that a contamination of impurities is avoided. The chemical solution for lithography (A) placed in the supply line is not brought into contact with an external environment (clean room atmosphere) until the chemical solution for lithography (A) is supplied on a semiconductor substrate (wafer) located in a coater. Usually, a plurality of filters to filtrate the chemical solution for lithography (A) is placed in a pipe which the chemical solution for lithography (A) passes through until the chemical solution for lithography (A) is applied onto the semiconductor substrate. Accordingly, the chemical solution for lithography (A) supplied to the semiconductor substrate passes through these filters to remove impurities (metals and particles), and then is applied onto the semiconductor substrate. Thus, the chemical solution for lithography (A) which passed through the filters for filtration is expected to contain no impurities. However, despite the careful handling as described above, a defect that may be derived from the applied chemical solution for lithography (A), presence of metal impurities in particular, is found on the semiconductor substrate onto which the chemical solution for lithography (A) is applied. These metal impurities existing on the surface of the semiconductor substrate may result in a defect after etching (cone defect) caused by the metal that becomes a mask when etching the semiconductor substrate, or may result in a defect (watermark) caused by bubble derived from the metal impurities contained. For manufacturing semiconductor device, these defects result in low yield of semiconductor device with good quality, and thus this issue needs to be solved as soon as possible.
The inventors of the present invention have made various investigations on the defects described above, and found that the metal impurities are not derived from the chemical solution for lithography (A) itself, but eluted from the filter to filtrate the chemical solution for lithography (A), which is one of the causes of the defects. One of the causes of the presence of metal impurities may be that a metal-containing catalyst used for manufacturing a resin that is a base material of the filter remains. Examples of the filter base material (resin) used in a filter to filtrate the chemical solution for lithography (A) include fluorine resins such as PTFE (polytetrafluoroethylene) and PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), PE (polyethylene), UPE (ultrahigh molecular weight polyethylene), PP (polypropylene), PSF (polysulfone), PES (polyethersulfone), and nylon. To synthesize these resins, a metal-containing catalyst such as a metal catalyst including titanium chloride and an organic aluminum compound or magnesium chloride, which is called the Ziegler-Natta catalyst; and a metal catalyst including a chromium compound such as chromium oxide, which is typified by the Phillips catalyst, is commonly used. Thus, metals derived from these catalysts may be one of the causes of the metal impurities.
Recently, the diameter of the pore (the size of the pore) of a filter to filtrate the chemical solution for lithography (A) becomes ultra-fine and is approximately from 30 nm to 2 nm.
To solve the problem of a defect found on the semiconductor substrate, a cleaning fluid that efficiently removes and cleans metal impurities and the like in a portion of a semiconductor manufacturing apparatus, in which the chemical solution for lithography (A) passes through the portion, is needed to be developed.
To date, examples of a cleaning fluid for manufacturing semiconductors include (1) universal cleaning fluid, (2) cleaning fluid for semiconductor substrates, (3) cleaning fluid for filters to filtrate a cleaning fluid, and the like.
Examples of (1) include: a cleaning fluid for lithography characterized by comprising at least one organic solvent selected from ketone organic solvents, lactone organic solvents, alkoxy benzenes, and aromatic alcohols (Patent Document 1); and a cleaning fluid for lithography comprising at least one organic solvent selected from glycol organic solvents, lactone organic solvents, alkoxy benzenes, and aromatic alcohols (Patent Document 2), which have been applied for patents. The cleaning fluids of these applications are characterized by being highly applicable to a plurality of cleaning steps, such as a step for removing an unnecessary chemical solution on the rear surface or the end of a substrate, or removing whole coating after the coating is formed on a base material; and a step for cleaning the base material before a coating material is applied thereon.
Examples of (2) include: a cleaning fluid containing (I) organic acid, (II) surfactant, and (III) inorganic acid (Patent Document 3); a cleaning agent for substrates comprising [I] an organic acid having at least one carboxyl group and/or [II] a complexing agent, [III] an organic solvent selected from the group consisting of (1) monovalent alcohols, (2) alkoxy alcohols, (3) glycols, (4) glycol ethers, (5) ketones, and (6) nitriles (Patent Document 4); a cleaning agent for manufacturing semiconductor devices, containing a fluorine compound and a glycol ether organic solvent (Patent Document 5); and a cleaning agent for semiconductor circuits comprising a carboxylic acid and a water-soluble organic solvent (Patent Document 6), which have been applied for patents. However, these cleaning fluids are designed to clean semiconductor substrates.
Examples of (3) include an 1% by weight hydrogen fluoride solution and an 1% by weight hydrochloric acid solution used as cleaning fluids in a method for desorbing metal ions chemically adsorbed on a filter by using an acidic chemical solution, in which the method is designed to clean a filter to filtrate a cleaning fluid used in a step for cleaning a semiconductor substrate (Patent Document 7), which has been applied for a patent. The portion for which a filter is used, which is described in Patent Document 7, is not the same as the portion through which the chemical solution for lithography (A) passes, which is the purpose of the present invention, but it relates to a filter for the portion through which a fluid to clean a substrate passes. The invention described in Patent Document 7 thus differs from the present invention.
As described above, the cleaning fluids described in any of the documents above have not been developed for removing metal impurities in the portion through which the chemical solution for lithography (A) passes. Thus, the cleaning fluids described in any of the documents above do not meet the purpose of the present invention, and effects thereof are unknown.